LITHOGRAPHIC APPARATUS, DEVICE MANUFACTURING METHOD, AND METHOD OF APPLYING A PATTERN TO A SUBSTRATE

• US 20110164229A1
• Filed: 12/15/2010
• Published: 07/07/2011
• Est. Priority Date: 12/23/2009
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Van De Kerkhof, Marcus Adrianus, STAALS, Frank
• Granted Patent: US 8,947,632 B2
• Time in Patent Office: Days
• US Class Current: 355/53
• CPC Class Codes: G03F 9/7003 Alignment type or strategy, e.g. leveling, global alignment
• CPC Class Codes: G03F 9/7034 Leveling

Abstract

A lithographic apparatus includes a patterning subsystem for transferring a pattern from a patterning device onto a substrate controlled in accordance with recorded measurements of level variations across a surface of the substrate. A level sensor is provided for projecting a level sensing beam of radiation to reflect from a location on the substrate surface and for detecting the reflected sensing beam to record the surface level at said location. The level sensor incorporates at least one moving optical element to scan the substrate surface by optical movement in at least one dimension to obtain measurements of surface level at different locations without mechanical movement between the level sensor and the substrate. Optical path length equalization measures may be employed, using shaped reflectors and/or additional moving mirrors, to avoid focus variation during the scan.

Claims

1. A lithographic apparatus comprising a patterning subsystem for transferring a pattern from a patterning device onto a substrate, the patterning subsystem being controlled in accordance with measurements of level variations across a surface of the substrate, the apparatus further comprising a level sensor for projecting a level sensing beam of radiation to reflect from a location on the substrate surface and for detecting the reflected sensing beam to record the surface level at said location, wherein said level sensor incorporates at least one moving optical element whereby said level sensor is arranged for optically scanning the substrate surface by the level sensing beam in at least one dimension to obtain measurements of the surface level at different locations without corresponding mechanical movement between the level sensor and the substrate.

2. An apparatus as mentioned in feature 1 wherein the scanning of said sensing beam extends in said one dimension across the entire substrate, and the substrate and the level sensor are arranged to move relative to one another in a second dimension to complete measurements of surface level variations in two dimensions.

3. An apparatus as mentioned in feature 1 or 2 said level sensing beam is a patterned beam, and the apparatus further comprises a focus control arrangement for maintaining focus of said patterned beam on said substrate during said level sensing beam scan as an indication of focus error.

4. An apparatus as mentioned in feature 3 wherein said focus control arrangement is responsive to level variations measured during at least one previous sensing beam scan as a predictor of focus error in a current scan.

5. An apparatus as mentioned in any of the preceding features 1-4 wherein said level sensor further includes at least one path length equalization optical arrangement configured to reduce variation of optical path length of said beam to the substrate surface during said sensing beam scan.

6. An apparatus as mentioned in any of the preceding features 1-5 wherein said moving optical element is positioned between elements of a lens system which projects the level sensing beam onto said substrate.

7. An apparatus as mentioned in any of the preceding features 1-6 wherein the level sensor includes at least two moving optical elements, movements of the elements being synchronized with one another.

8. An apparatus as mentioned in feature 7 wherein a first moving optical element steers the level sensing beam onto a target location moving across the substrate surface and a second moving optical element steers the level sensing beam reflected from said moving target location to a stationary detector.

9. An apparatus as mentioned in feature 7 or 8 wherein at least two moving optical elements are positioned in series between a source of said level sensing beam and said substrate, said elements moving synchronously to steer said beam onto a target location moving across the substrate while minimizing optical path length variation.

10. An apparatus as mentioned in feature 9 further comprising a projection lens system which projects the level sensing beam onto said substrate, wherein neither of said two moving optical elements is positioned between elements of said projection lens system.

11. An apparatus as mentioned in any of the preceding features 1-10 wherein said level sensing beam follows a path in which it is reflected twice from said substrate surface and twice from each said moving optical element for each height measurement.

12. An apparatus as mentioned in any of the preceding features 1-11 of the type which transfers said pattern from said patterning device to said substrate through an optical projection system in an exposure step, apparatus being responsive to the substrate level variations measured by said level sensor in a prior measurement step in order to maintain focus of the projected pattern at a target portion of the substrate.

13. A device manufacturing method comprising transferring a pattern from a patterning device onto a substrate using a lithographic apparatus as mentioned in any of the preceding features 1-12, the method comprising the steps:

loading a patterning device and a substrate into the apparatus;

measuring surface level variations across the substrate using said level sensor;

transferring the pattern one or more times from the patterning device to the substrate, controlling said transferring step by reference to the measured surface level variations; and

processing the patterned substrate to produce functional device features.

14. A method of measuring level variations across a surface of substrate in a lithographic apparatus, the method comprising:

(a) providing a level sensing optical system in the lithographic apparatus;

(b) using said optical system to project a level sensing beam of radiation to reflect from a location on the substrate surface; and

(c) detecting the reflected sensing beam to record the surface level at said location,

wherein the optical system employs at least one moving optical element whereby in step (b) said sensing beam scans different locations across the substrate surface by optical movement in at least one dimension, and in step (c) the detecting obtains respective measurements of surface level at said different locations without corresponding mechanical movement between said level sensing optical system and the substrate.

15. A method as mentioned in feature 14 wherein the optical scanning of said sensing beam is extends in said one dimension across the entire substrate, the substrate and level sensing optical system being moved relative to one another in a second dimension direction to complete measurements of surface level variations in two dimensions across the substrate.

16. A method as mentioned in features 15 or 16 wherein said sensing beam is a patterned beam, the method including focusing said patterned beam on said substrate by reference to level variations measured during said optical scanning as an indication of focus error, wherein said focusing is performed by reference also to level variations measured during at least one previous scan as a predictor of focus error in a current scan.

17. A method as mentioned in any of the features 14 to 16 wherein said level sensing optical system further includes at least one path length equalization arrangement for reducing variation of optical path length of said beam during said scanning.

18. A method as mentioned in feature 14, 15, 16 or 17 wherein said moving optical element is positioned between elements of a projection lens system which projects the level sensing beam onto said substrate.

19. A method as mentioned in any of the features 14 to 18 wherein the level sensing optical system includes at least two moving optical elements, movements of the elements being synchronized with one another.

20. A method as mentioned in claim feature 19 wherein at least two moving optical elements are positioned in series between a source of said level sensing beam and said substrate, said elements moving synchronously to steer said beam onto a target location moving across the substrate while minimizing optical path length variation.

21. A method as mentioned in feature 20 wherein neither of said two moving optical elements is positioned between elements of a projection lens system which projects the level sensing beam onto said substrate.

22. A method as mentioned in any of the features 14 to 21, further comprising (d) transferring said pattern from said patterning device to said substrate through an optical projection system in an exposure step, said transferring step (d) being controlled by reference to the substrate level variations measured in steps (b) and (c) in order to maintain focus of the projected pattern at a target portion of the substrate.

23. A computer program product containing one or more sequences of machine-readable instructions for controlling a level sensor optical system and level sensor signal processing units in a lithographic apparatus, the instructions being adapted for implementing the steps (b) and (c) of a method as mentioned in any of the features 14 to 22.